Is there any way we can restrict duplicate entries in core data?

Question

I have been trying to add objects in core data. So, i want that it should not allow duplicate entries in core data store. How to do that? This is my code related to save data.

  -(IBAction)save:(id)sender
    {

        if([name.text isEqualToString:@""] && [address.text isEqualToString:@""] && [phone.text isEqualToString:@""])
        {

            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Yo..!"
                                                        message:@"Data Not Saved"
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
            [alert show];
        }
    else
    {
        coreDataAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

        NSManagedObjectContext *context = [appDelegate managedObjectContext];


        NSManagedObject *newContact;
        newContact = [NSEntityDescription
                      insertNewObjectForEntityForName:@"Contacts"
                      inManagedObjectContext:context];


        [newContact setValue:name.text forKey:@"name"];
        [newContact setValue:address.text forKey:@"address"];
        [newContact setValue:phone.text forKey:@"phone"];


        name.text = @"";
        address.text = @"";
        phone.text = @"";

        NSError *error;
        [context save:&error];

        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Yo..!"
                                                    message:@"Data Saved"
                                                   delegate:nil
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles:nil];
        [alert show];

         NSLog(@"Object Saved\n");

    }


}

Answer 1

As there is no built in method available, you need to fetch results and check whether result contains object you don't want to be duplicated.

Here is code snippet:

-(void)checkForDuplicates
{
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Students"
                                          inManagedObjectContext:managedObjectContext];

    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setEntity:entity];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"students"
                                                               ascending:NO];
    NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

    [request setSortDescriptors:sortDescriptors];
    [sortDescriptor release];

    NSError *Fetcherror;
    NSMutableArray *mutableFetchResults = [[managedObjectContext
                                        executeFetchRequest:request error:&Fetcherror] mutableCopy];

   if (!mutableFetchResults) {
        // error handling code.
    }

    if ([[mutableFetchResults valueForKey:@"users"]
         containsObject:name.text]) {
        //notify duplicates
        return;
    }
    else
    {
         //write your code to add data
    }
}

Hope this may help you!

Answer 2

no, coredata has no built-in in uniquing as it isn't a DB.

---

you have to assure uniqueness in your program logic.

e.g. often, one does a fetch for an entry that should be unique and if that fetch has 1 entry, don't add another, else add it!

==> this works well for serial CD access, but can get complicated with multiple contexts that run in a multithreaded env